Conventionally, an in-vehicle device such as an in-vehicle navigation device includes a hard disk drive. The in-vehicle device shows a map around a current position of a vehicle on a display based on a map data. Further, the in-vehicle device calculates an optimum route to a destination so that the in-vehicle device guides a driver for a driving direction. The hard disk drive as a memory stores the map data and the like. Since the hard disk drive has a large amount of storage capacity, the hard disk drive stores not only the map data but also application software for operating the navigation device, and a music data and/or an image data for being utilized in an audio device, which is integrated with the navigation device.
The hard disk drive is a memory for recording and reading out information by using a magnetic head and a disk. The disk as a memorizing means is prepared by applying magnetic material on the disk. When the hard disk drive operates, the disk rotates with high speed, and the magnetic head floats over the disk because of pressure of air, which is pulled by the rotating disk so that the air also rotates. A distance between the magnetic head and the disk is small when the magnetic head floats over the disk. Accordingly, under a condition that environmental air pressure is very low, the distance between the head and the disk may not be sufficient when the hard disk drive operates. This is because the air pressure for floating the magnetic head is low. Thus, the head may hit on the disk so that the disk is damaged. The air pressure becomes low with increasing altitude from sea level. Therefore, the hard disk drive has service altitude limit. In general, operation guarantee of the hard disk drive with respect to the altitude is about three thousands meters (i.e., about 0.7 atm) to five thousand meters (i.e., about 0.5 atm).
Accordingly, when the in-vehicle device has the hard disk drive, it is necessary to protect the hard disk drive from damage when the in-vehicle device is used in a high land such as a 3000 meters high road, and a 4000 to 5000 meters road. In the high land, the altitude of the land exceeds the altitude limit of the hard disk drive.
When the vehicle runs on a road, the altitude of which is equal to or higher than a predetermined altitude, a part of the map data stored in the hard disk drive is transferred to an external memory. Then, the hard disk drive stops to operate, and the in-vehicle device shows a driving route based on the map data stored in the external memory when the vehicle runs on the high land having the altitude higher than the predetermined altitude such as 3000 meters. This technique is described in U.S. Pat. No. 7,171,305. Thus, by stopping the operation of the hard disk drive, the hard disk drive is protected from damage, and the in-vehicle device continues to guide the route.
Although the technique in U.S. Pat. No. 7,171,305 can protect the hard disk drive when the vehicle runs in the high land. However, if the in-vehicle device turns on at the high land, it may be difficult to protect the hard disk drive from the damage. Specifically, the above technique does not guarantee the protection of the hard disk drive when the in-vehicle device turns on initially when the vehicle is located in the high land, i.e., the above technique does not guarantee the activation of the in-vehicle device at the high land. Therefore, there are difficulties as follows.
In the conventional in-vehicle device having the hard disk drive, the data such as program is read out from the hard disk drive, and then, the data is transferred to a working memory such as a RAM. Based on the data of the working memory, the device runs. If operation data just before the end of operation at the last time is stored in the working memory, the device can be activated based on the operation data stored in the working memory without reading the data from the hard disk drive. The working memory used for the above usage is formed from a volatile memory, which requires electricity to hold to store the data therein, since it is required for the working memory to have high access speed and the like. Here, when the in-vehicle device stops to operate, the electricity for the working memory, i.e., standby power is supplied from an in-vehicle battery.
However, the battery of the vehicle may be down when the vehicle stops driving, or the power source circuit is shut down for maintenance. In this case, the standby power is not supplied to the working memory, and thereby, the data in the memory may be disappeared. Thus, when the in-vehicle device starts to operate for the next time, it is necessary to read out the program and the like from the hard disk drive and to input the program and the like into the working memory. At this moment, when the vehicle is located at the high land, the program for prohibiting the operation of the hard disk drive at the high land is also disappeared from the working memory. Accordingly, even when the current location of the vehicle is at the high altitude place, the hard disk drive is activated in case of start-up of the in-vehicle device. As a result, since the hard disk drive is activated at the high altitude place, the hard disk drive may be broken.
Thus, it is required for the hard disk drive mounted in the vehicle to protect it from breakdown even when the hard disk drive suddenly starts to function at the high altitude place.